As discussed on the Gibberlings3 forum, these are the changes I have made to AreaProperties.cpp.
1. Open Location Front/Back. If you have selected one of these then selecting the other will default the cursor to the already-selected position.
2. Door polygons. When selecting a door to draw either the open or closed polygon, the cursor will default to the position set by Open Location Front above.
There are three sets of code changes to the file; search for 'yovaneth'.